The present invention generally relates to a method and an apparatus for cleaning a wafer container and more particularly, relates to a method for dry cleaning a wafer container that is equipped with a bottom mounting plate covered with contaminating particles by first mounting the container in an enclosure and then blowing an inert gas or air on the bottom mounting plate and simultaneously withdraw by vacuum the inert gas or air that contains contaminating particles.
In the recent development of semiconductor fabrication technology, the continuous miniaturization in device fabricated demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 xcexcm range, a cleanliness class of 100-1000 (which means the number of particles at sizes larger than 0.5 xcexcm per cubic foot) was sufficient. However, when the feature size is reduced to 0.25 xcexcm, a cleanliness class of 0.1 is required. It has been recognized that an inert mini-environment may be the only solution to future fabrication technologies when the device size is reduced further. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness mini-environment that is constantly flushed with ultrapure nitrogen that contains no oxygen and moisture.
Different approaches in modern clean room design have been pursued in recent years with the advent of the ULSI technology. One is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16M and 64M DRAM products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered. This stringent requirement creates a new mini-environment concept. Within the enclosure of the mini-environment of a process tool, an extremely high cleanliness class of 0.1 (which means the number of particles at sizes larger than 0.1 xcexcm per cubic foot) is maintained, in contrast to a cleanliness class of 1000 for the overall production clean room area In order to maintain the high cleanliness class inside the process tool, the loading and unloading sections of the process tool must be handled automatically by an input/output device known as a SMIF (standard mechanical interface) apparatus. A cassette of wafer can be transported into the process tool by a SMIF pod situated on top of a SMIF apparatus.
A conventional SMIF apparatus consists of a robotic transfer system or a robotic arm which is normally configured for gripping the top of a cassette from a platform on which the cassette is placed (inside a pod). The robotic arm, sometimes is replaced by a gripper assembly, is capable of transporting the cassette into the process tool and place it on a platform vertically such that the cassette is oriented horizontally. At the beginning of the process, an operator positions a SMIF pod on top of a SMIF arm port which contains a cassette for holding a large number of wafers in an upright position. The SMIF arm port then descends into the SMIF apparatus for the robotic arm to transport the cassette into the process tool. The SMIF system is therefore capable of automatically utilizing clean isolation technology to maintain a high class clean room effectiveness near wafers and processing equipment. The operation of the robotic arm or the gripper is controlled by an ancillary computer (not shown) or by the process tool. The cassette carries wafers or other substrates that are being processed.
Referring initially to FIGS. 1A and 1B, wherein the top view of a SMIF arm port 10 is shown in FIG. 1A while a bottom view of a SMIF pod 20 is shown in FIG. 1B. In the bottom view of the SMIF pod 20, a bottom mounting plate 22 is used for matching to the SMIF arm port 10 on its top surface 12. At the beginning of a wafer loading process, an operator positions SMIF pod 22 on top of the SMIF arm port 10. The mating process for the two surfaces 12, 22 is carried out by human hands and therefore, friction between the two surfaces 12, 22 cannot be avoided. To accomplish the mating process, the locating pins 14 on the SMIF arm port surface pod 12 must penetrate the apertures 24 on the bottom mounting plate 18. A mechanical locking device 16 located on the top plate surface 12 of the SMIF arm port 10 must further be aligned with the pod lock alignment hole 26 on the bottom mounting plate 18 of SMIF pod 20. During the mating operation of the two surfaces 12 and 22, frictional forces between the surfaces generates particles in between the surfaces. The most likely areas that cumulate particles are areas close to the locating pins 14 and close to the pod lock 16. For instances, the shaded areas 28 shown in FIG. 1A illustrate typical locations where particles contaminations occur.
While SMIF pods are normally cleaned in a wet cleaning process by utilizing deionized water or other cleaning solvents periodically during a preventive maintenance procedure. The wet cleaning is only used to clean the wafer cassette positioned inside the SMIF pod and the interior surfaces in the pod. Due to the presence of mechanical components in the SMIF arm port 10 and on the SMIF pod bottom mounting plate 20, i.e., the pod lock 16 which is fabricated of metal, the SMIF arm port 10 and the bottom mounting plate 20 of the SMIF pod can not be cleaned in a wet cleaning process in order to prevent corrosion and other deteriorating effects caused by the cleaning solvent.
Presently, the surfaces on the SMIF arm port 10 and on the bottom mounting plate 20 of the SMIF pod can only be cleaned by manually wiping the surfaces with a dustless cleaning cloth, or with a dustless cleaning cloth wetted with isopropyl alcohol. However, the surface wiping method does not thoroughly clean the particles on the SMIF arm port or on the bottom mounting plate.
While other cleaning methods for the SMIF arm port and for the bottom mounting plate have been proposed, none of them is effective in correcting the particle contamination problem. For instance, others have proposed the use of adhesive tape to remove particles from the surfaces. However, residual adhesive from an adhesive tape left on the surfaces may cause more severe contamination problem. A rolling brush has also been used to remove particles from the bottom mounting plate of a SMIF pod, however, the brush generates electrostatic electricity which leads to further accumulation of particles.
It is therefore an object of the present invention to provide a method for cleaning a wafer container that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for cleaning the bottom mounting plate of a wafer container that does not require a wet cleaning process.
It is a further object of the present invention to provide a method for cleaning the bottom mounting plate of a wafer container that can be carried out either with or without wafers in the container.
It is still another object of the present invention to provide a method for cleaning the bottom mounting plate of a SMIF pod that can be easily carried out without causing a fabrication yield loss.
It is another further object of the present invention to provide a method for cleaning the bottom mounting plate of a SMIF pod that can be easily carried out by mounting the pod in an enclosure.
It is yet another object of the present invention to provide a method for cleaning the bottom mounting plate of a SMIF pod that only requires a high pressure air or inert gas and a factory vacuum source.
It is still another further object of the present invention to provide a n apparatus for cleaning the bottom mounting plate of a wafer container that includes an enclosure for mounting the wafer container thereto, a conduit for supplying a high pressure air or inert gas, and a conduit for supplying a factory vacuum.
In accordance with the present invention, a method for cleaning a wafer container equipped with a bottom mounting plate and an apparatus for cleaning the wafer container are disclosed.
In a preferred embodiment, a method for cleaning a wafer container equipped with a bottom mounting plate can be carried out by the operating steps of providing an enclosure that has a top panel equipped with at least one opening for positioning a wafer container therein, four side panels and a bottom panel forming a substantially air-tight cavity; mounting a wafer container equipped with a bottom mounting plate covered with contaminating particles in the opening in the top panel of the enclosure such that the bottom mounting plate is substantially exposed to the cavity; directing a first flow of air or inert gas toward the bottom mounting plate to dislodge the contaminating particles; and withdrawing a second flow of air or inert gas containing the contaminating particles into a factory vacuuming system.
The method for cleaning a wafer container that is equipped with a bottom mounting plate may further include the step of providing the top panel with two openings for positioning two wafer containers therein. The method may further include the step of providing at least one air or inert gas feed conduit and at least one factory vacuum line conduit through the bottom panel of the enclosure. The method may further include the steps of providing an exhaust opening in the bottom panel and connecting the exhaust opening to factory exhaust. The method may further include the step of directing the first flow of air or inert gas toward the bottom mounting plate in a preset scanning mode, or the step of directing the first flow of air or inert gas toward the bottom mounting plate at a pressure of at least 5 psi.
The method for cleaning a wafer container that is equipped with a bottom mounting plate may further include the step of withdrawing the second flow of air or inert gas containing the contaminating particles into the factory vacuum system maintained at a pressure not higher than 740 mmHg. The method may further include a step of directing a first flow of an inert gas selected from a gas consisting of nitrogen, helium and argon towards the bottom mounting plate to dislodge the contaminating particles. The method may further include the step of directing a first flow of an inert gas of nitrogen toward the bottom mounting plate to dislodge the contaminating particles, or the step of directing a first flow of air or inert gas and the step of withdrawing a second flow of air or inert gas are executed simultaneously.
The present invention is fir further directed to an apparatus for cleaning a wafer container that is equipped with a bottom mounting plate which includes an enclosure formed by a top panel that has at least one opening adapted for positioning a wafer container therein, four side panels and a bottom panel forming a substantially air-tight cavity; at least one wafer container equipped with a bottom mounting plate covered with contaminating particles positioned in at least one opening of the enclosure with the bottom mounting plate substantially exposed to the cavity; a first conduit installed through the bottom panel for feeding a purge gas into the cavity towards the bottom mounting plate and for dislodging the contaminating particles from the bottom mounting plate; and a second conduit installed through the bottom panel for withdrawing the purge gas containing the contaminating particles from the substantially air-tight cavity.
In the apparatus for cleaning a wafer container that is equipped with a bottom mounting plate, the contaminating particles may be generated by friction between the bottom mounting plate of the wafer container and the wafer container port. The apparatus may have two openings in the top panel of the enclosure for accommodating two wafer containers, two first conduits and two second conduits. The second conduit may be a vacuum conduit in fluid communication with a factory vacuum source. The purge gas may be a gas selected from the group consisting of air, nitrogen, helium and argon. The purge gas may have a pressure of at least 5 psi. The second conduit may be connected in fluid communication with a factory vacuum source that has a pressure of not higher than 740 mmHg. The second conduit may be installed juxtaposed to the first conduit.